Communication system



March 14, 1939. H. J. NICHOLS ET AL COMMUNICATION SYSTEM Filed Feb. 23,1955 2 Sheets-Sheet 1 R50 T/ F/ER ATTORNEYS March 14, 1939.

H. J. NICHOLS ET AL COMMUNICATION SYSTEM Filed Feb. 23, 1935 2Sheets-Sheet 2 RECTIFIER REC T/F/ER F/LTER Pam/rm a9 lNVENTCgQf W( Eff/35M 9 ATTORN EYS Patented Mar. 14, 1939 UNITED STATES 2,150,241COMMUNICATION SYSTEM Harry J.

Nichols and Henry L. Tholstrup, Dayton, Ohio, assignors, by direct andmesne assignments, to International Business Machines Corporation, NewYork, N. IL,

New York a corporation of Application February 2a, 1935, Serial No.7,674 r 6 Claims.

This invention relates to communication systems, and particularly tocarrier telegraph systems.

It is the principal object of the invention to 5 provide a verysatisfactory carrier communication system making use of simple andeconomical apparatus.

A further object is to provide a carrier system having a minimum ofsteps or links in the system.

A further object is to provide a carrier system particularly adapted totelegraph systems utilizing signals of uniform duration but of differentcharacteristics.

A further object is to provide a carrier system in which frequencies aregenerated, amplified, and the like in groups, each group being handledin such manner as to obtain compensation of certain variations in therelations between the signals of the several frequencies. 20 A furtherobject is to provide a carrier system particularly adapted tosimultaneous telephonic and telegraphic communication over the samecircuit.

Other objects and features will be in part obvious and in part hereafterpointed out in connection with the following description, theaccompanying drawings, and the appended claims.

In the drawings:-

Fig. 1 shows in schematic representation a preferred. form of sendingcircuit illustrating one aspect of the invention;

Fig. 2 shows one form of receiving circuit according to the invention;

Fig. 3 shows another form of receiving circuit according to theinvention; and

Fig. 4 shows a combined sending and receiving arrangement embodying thecircuits of Figs. 1 and 3.

In the several figures, like characters represent like parts.

Referring now to Fig. 1 oscillator tube To is preferably of thetwin-triode vacuum tube type being provided with two grids H and I2, twoanodes 2|, 22, and a common thermionic cathode l3 all mounted in anevacuated envelope M in well known manner. Power for tube To and theother tubes employed in. the various circuits is obtained from arectifier and filter unit l5 as indicated, or from any other suitablesource. The voltage divider of unit I5 is provided with the propersections, as for example l5a, l5b, l5c, or is suitably tapped to providethe proper potentials to the various circuits of the arrangement.Oscillator tube To is provided with two tuned oscillator circuits ofknown type, one circuit designated by reference numeral H beingassociated with grid ll, while similar circuit I2 is associated withgrid l 2. Inductively coupled with these circuits are feed-back circuits2|, and 22', associated with anodes 2| and 22 respectively formingoscillation transformers 0T1 and GT2, respectively. Oscillator circuit ll is tuned to a particular frequency f1 while oscillator circuit I2 istuned to a difierent frequency f2. These are known as the channelfrequencies, and in cases where simultaneous telephone and telegraphcommunication are to be provided over the same circuit, thesefrequencies are preferably chosen in the range just above the usualaudible telephonic frequencies, as for example in the range between tenand twenty kilocycles. Where telephonic communication is not involved,the frequencies are advantageously chosen in the audible range sincefollowing well known laws, the lower frequencies are more eflicientlytransmitted over wire circuits. The invention is not, of course,restricted to any particular frequencies or frequency ranges, nor is itrestricted to the provision of two channel frequencies and circuits, asmore may be provided if desired.

Grids l l and I2 are normally held at a negative bias by section l5b ofthe voltage divider, the bias being suificient to prevent oscillation.The normal bias is applied through resistors R11, R12, while by-passcapacitors C, C" offer a low impedanc'e return of the oscillating gridcurrents to cathode.

The keying equipment is connected across the grid-cathode circuits ofoscillator tube To. Thus, for example, the circuit including key K1,resistor R11, and battery 13 may be regarded as the sending loop ofchannel one, while the circuit including key K2, resistor R12 andbattery B may be regarded as the sending loop of channel two. Bothoscillation circuits are coupled to the line by suitable means such asline transformer T15. Blocking capacitor C5 is provided to preventdirect current from the line saturating transformer Tr5, but is notessential on lines where stray currents are not likely to occur. Thesending circuit, consisting of the secondary of T15 and C5 in seriestherewith is preferably bridged across the line head of telephoneinstruments when used. Suitable means, such as choke L5, is preferablyconnected in series with the telephone instruments for the purpose ofimpeding the passage of carrier currents in that direction whilepermitting the passage of voice currents to.the telephone instruments.

The operation of the circuit shown in Fig. 1 is as follows:--Normal1yoscillator tube To is prevented from oscillating by reason of thenegative bias on its grids. Assume that the key K1 is closed, completingthe sending loop circuit. Then current from battery B flows through K1and R11 and return via the grounded frame, setting up a voltage acrossR11 opposing the bias voltage and raising the potential of grid llsufficiently to cause To to build up oscillations in the circuit l lassociated with grid H. Oscillations of frequency ii are thentransferred to the line via line transformer Tr5. As soon as the key isreleased the original bias on grid II is returned, and the oscillationsare promptly stopped. Thus a train of waves of frequency fl istransmitted over the line so long as key K1 is held down, and suchcarrier signals represent the signal pulses in the sending loop asregards time and duration. Assuming key K: to be depressed, the actionis similar except that the potential of grid I2 is raised positively andcarrier signals of frequency Ia are transmitted to the line.

It should be observed that the arrangement herein shown eliminates theneed for an amplifying tube, with a consequent saving in apparatusalthough such amplifying means as desired may be used. It also presentsa novel method of keying carrier generating apparatus. Fur thermore,since the same oscillator tube generates a plurality of frequencies,there is an inherent compensation of variations likely to occur were thefrequencies generated by separate tubes. For example, a common cathodeand a common atmosphere for the plural elements of the tube areconducive to uniformity of emission and space currents. As the tubeages, the constants of the tube circuits are affected in the samedegree, hence the power ratio of the oscillating currents tends toremain balanced, thus maintaining a uniform ratio of the signals. Thetuning and balancing of the I circuits is facilitated by the uniformityof the characteristics of the plural tube circuits. There is alsoasaving in power, a saving in space and in associated parts.

Referring now to form of receiving arrangement, the receiving circuit 20is coupled to the line by line transformer T in the same manner as inthe previous figure or by other suitable means. wise, inductance L5offers a high impedance to the carrier signals in the direction of thetelephone instruments with relatively minor attenuation of the voicecurrents. The receiving aircult!!! is divided into two branches and 20"tuned to frequencies 11 and In by series combinations of capacity andinductance, C1, L1 and C2, L2, respectively. The primaries oftransformers TH and Tr2 are included in branch circuits 20' and 20", andthe secondary circuits of these transformers are tuned to frequenciesf1, and I: by capacitors C3 and C4 respectively. Transformers Trl andTrZ couple the tuned branch circuits to the grids of electronic relaysT1 and T: as shown. The L/C ratio or ratio of inductance to capacity ofthe tuned circuits including C3 and C4 should preferably be small inorder that the full resonant response of the tuned circuits will besomewhat delayed. This counteracts the tendency of transient impulses totrip T1 and T2.

Electronic signal translating devices comprising relays T1 and T2 arepreferably of the well known triode gas-discharge tube type in which thegrid trips or ionizes the tube permitting a. comparatively largeionization current to flow in the anode-cathode circuit thereof. Afterionization, the grid loses control and is ineffective to terminate thedischarge until the anode potential is reduced substantially to zero.Hence deionizing or cut-ofi means additional to the grid are providedwhen direct current is used to supply the anode circuit. Any suitablemeans may be used, such means being indicated by reference numeral 25.For example, a cut-oil relay Fig. 2, representing one Likemay be used inthe position of when the tubes are used alternately, to effectdeionization of the tube or interruption of the circuit after a briefinterval of operation, thus serving both tubes, or other known means maybe used. Resistors R1, R2 serve to limit the grid current uponionization of their associated relays, while resistors R3, R4 representthe load resistances of T1 and T2 respectively. Relays L3, Lr'mayrepresent the receiving relays for two channels, two printer actuatingmagnets, or any other translating means by which the telegraphic signalsare recorded or rendered intelligible. Relays T1 and T2 are convenientlysupplied with energy by rectifier unit H5, or from any other suitablesource.

The operation of the arrangement of Fig. 2

is as follows: Assume that a train of carrier waves of frequency i1 isreceived from the line. Owing to the tuned filter arrangement L1, C1 inbranch circuit 20', this branch offers a markedly lower impedance to thesignal train than does branch 20''. Hence the voltage which ap pearsacross the secondary of TM is considerably higher than that across thesecondary of M. Furthermore the secondary of Tri being tuned tofrequency )1, While the secondary of T11 is tuned to frequency is, afurther frequency selective effect is obtained. For example, undersuitable conditions, for signals of frequency 11 the voltage ratio ofthe potential applied to the grid of T1 as compared to the potentialapplied to the grid of T2 may be 10 to 1, while a like ratio favorableto T2 may be obtained for signals of frequency f2. Thus by suitablechoice of the operating conditions for T1 and T2, following well knownpractice, T1 will be exclusively tripped by signals of frequency f1,while T2 will be exclusively tripped by signals of frequency is.

Assuming that T1 has thus been tripped, a pulse of current flows(following the ordinary convention) from positive source via cut-offdevice 25 to the anode of T1, thence by space current to cathode,through resistor R3 to frame and return to source. The current throughresistor R3 causes a potential drop across same, hence part current (insuch amount as is desired) is diverted through the winding of relay L3energizing same. After an interval determined by cut-oil, device 25, thepotential across the anode and cathode of T1 is reduced substantially tozero, the potential being held down long enough to permit the grid of T1to regain control, thus effecting the de-ionization of T1.

In similar manner, .upon the reception of a train of waves of frequencyf2, T2 is ionized, relay L1 is energized and cut-off device 25 causesthe deionization of T2 thus restoring the circuit to normal condition.

It should be noted that the cut-off device operates to effectdeionization after a definite, predetermined interval, hence thetranslating devices are energized for the same duration by all signalsof amplitude suificient to ionize the electronic relays. The inventionis thus particularly suitable to equal signal systems, and in suchsystems has the practical advantage of providing reliable operatingimpulses even though the received signals may be clipped or mutilated.

The arrangement here shown is very desirable in that among otheradvantages, it eliminates the need for a detector and/or amplifyingtube,

the electron relays which perform the .usual function of a line relaybeing actuated directly by the incoming signals. It is characterized byits simplicity-and advantageous use of electron relays. In addition tothe selective action of the tuned receiving circuits, further selectiveaction is obtained by the novel method of selective tuning of theelectron relay input circuits.

Referring now to Fig. 3 which shows another form of receivingarrangement in accordance with the invention, selection as to frequencyis accomplished in steps, the first of which occurs in the couplingcircuits of tube T whichhere functions as a signal amplifying tube. Thearrangement'shown is particularly suitable for use on lines where theattenuation is considerable and/or where the channel frequencies arenarrowly spaced. The secondary circuit 20 of line transformer Tr has twobranch circuits 20', 20" including coupling coils 2|, 22' oftransformers O'Ifi and GT2, these branch circuits being selectivelytuned to frequencies )1 and f2 by suitable means such as filterarrangements S1,L1andQ2,L2'. The secondaries of OTI and GT2 are alsotuned to frequencies f1 and f2 respectively, and apply potentialvariations corresponding to the carrier signals to grids H and I2 oftube To. The primaries of transformers Trl and Tr2 are included in platecircuits 3| and 32 associated with plates 2| and 22 respectively. Theremainder of the arrangement is as described in connection with Fig. 2.

The operation is as followsz-Carrier signals from the line aretransferred by line transformer Tr5 to branch circuits 20' and 20", butin unequal degree depending upon the carrier frequency, as for examplesignals of frequency h are offered a low impedance path by fil tercombination L1, 01 and a high impedance path by filter combination L2,C2, hence the major portion of the energy flows in circuit 20. Forsignals of frequency f2 the reverse holds. Further selective actionoccurs in tuned circuits H and i2 improving the voltage ratio of thepotentials applied to grids H and I2. Tube To amplifies the signals,which are applied with augmented amplitude to the primaries oftransformers TH and Tr2. With proper operating conditions, T1 will thusbe tripped by h signals, and T2 by fz signals, producing selectiveoperation of translating devices L3 and L4.

This arrangement is characterized by its high selection ratio, itsability to function reliably on weak signals, its economy of apparatus,and the inherent compensatory features of the twin amplifying tubeemployed.

It should be noted that amplifying tube To has the beneficial effect ofincreasing the selection margin. As-is well known, electron relays suchas T1 and T2 here employed are tripped by a certain critical value ofpotential. For example, let it be assumed that each tube can be trippedby a peak potential of twenty volts applied to the primaries of Tri andT72. Let it further be assumed that the selection ratio due to tunedcircuits L1, C1, and L2, 02 and tuned transformers QTl and GT2 is ten toone, and that the effective amplification factor of To is five. Then ifthe peak voltage on grid it due to a fi signal is volts, that on grid 52will be one volt, giving a selection margin of nine volts. Afteramplification by tube To, these peak voltages become 50 volts andb voltsrespectively, giving a selection margin of 45 volts. This voltagedifference, applied to T1 and T2 bytransformers TM and TrZ, provides asubstantial operating margin for selection purposes. It is to beunderstood that the voltage values cited in the example are forillustrativepruposes, and in practice reliable selec tive action can beobtained with comparatively feeble carrier signals, and widely varyingselective ratios.

Referring now to Fig. 4, a combined sending and receiving arrangement isshown which is particularly adapted to two way systems in whichcommunication is held in one direction or the other, but notsimultaneously in both directions. This arrangement represents acombination of those shown in Figs. 1 and 3.

Suitable switching means, designated by S, Si,

S2, S3, are provided to change the circuits at will from sending toreceiving condition. The switches are shown at convenient places in thediagram, but in practice are conveniently grouped in a single multipleswitch. It is assumed that when the switch tongues are moved to theright, the circuits are in sending condition and when moved to the leftare in receiving condition. ,Assuming first that sending conditions areto be established, all switch. tongues are to be considered as being tothe right. Switch S then applies positive potential to plate 2| via lead20, primary of Tr5, branch 20 and coil 2|, via switch SI, and thence toplate 2|; and to plate 22 through the circuit including the primary ofTr5, thence through branch 20" and coil 22, via switch S2 to plate 22.Switch S3 connects the sending device, such as printed 34, across gridresistor R via lead 4|, and across grid resistor R|2 via lead 42. Aprinter which has been found to give very satisfactory results is thatdisclosed in our copending application Serial No. 738,833, filed August7, 1934;

The sending operation is the same as described in connection with Fig.1, except that printer 34 functions in the same manner as but replacesthe keying arrangement comprising Kl, K2, and B of Fig. l. Briefly, oneportion of the printer circuits is associated with OTI and the otherportion with 0T2. When one of the printer keys is operated, the tube Tois-placed in oscillation at the selected frequency, f1 or f2, and forthe proper duration and at the proper time in accordance with theparticular key operated, a corresppnding signal being sent over theline.

Assuming next that receiving conditions are to be established, allswitch tongues are moved to the left. Switch S connects lead 20 to, themid point between Cl, C2; switch Sl connects plate iii to lead 3|, andcoil 2| to L|; while switch S2 connects plate 22 to lead '32 and coil 22to L2, thus completing the signal circuits as described above inconnection with Fig. 3. Switch S3 connects printer 34 to leads 5% and 52which are included in the output circuits of electron relays Ti and T2.

The receiving operation is the same as that described in connection withFig. 3, except that printer 3t functions in the same manner as butreplaces the translating devices L3, L4 of Fig. 3. Thus the signals,distinguished by their frequency, time, and/or duration, are caused toeffect the selective operation of the printer and to cause operation ofthe printer keys corresponding to those at the sending station.

The arrangement is characterized by its dual utility, relativesimplicity, and balancing and compensating features.

It ll be apparent that the arrangements shown in Figs. 1 and 2 can becombined into a sending-receiving unit in the same general manner as thearrangements of Figs. 1 and 3 have been combined, and in someapplications may be preferable to that shown in Fig. i. detailedconnections for such combination will readily be seen by those skilledin the art, hence further description is not required.

The advantages enumerated, and others unmentioned, are attributable tothe method of handling the channel frequencies in groups, to the use ofa multiple tube with balanced elements, to the advantageous use ofelectron relays in combination with frequency selective circuits, and tothe novel arrangements disclosed. It will be apparent that the inventionprovides a carrier signalling system which is relatively simple,economical in the use of apparatus, efllcient and reliable in action,and which meets in a highly satisfactory manner the manifold andexacting requirements for a system of this type.

While the methods herein described and the forms of apparatus forcarrying these methods into eifect constitute preferred embodiments ofthe invention, it is to be understood that the invention is not limitedto these precise methods and forms of apparatus, and that changes may bemade in either without departing from the scope of the invention whichis defined in the appended claims.

,What is claimed is:

1. In carrier signalling systems, a carrier frequency selectivereceiving arrangement comprising a plurality of frequency selectivereceiving circuits each tuned to a particular frequency, a plurality ofelectron discharge tubes each provided with a control grid and adaptedto be substantially completely ionized upon the direct application of asignal having a critical value of potential to its control grid,magnetic coupling means for coupling said selective receiving circuitsto the grids of said discharge tubes, said magnetic coupling means beingprovided with a tuned secondary circuit characterized by an L/C ratioadapted to retard the resonant response of said tuned circuit, aplurality of signal translating means each operatively associated withthe discharge circuit of one of said discharge tubes, a source of directcurrent for applying operating potential to said discharge tubes, anddischarge current terminating means associated with said discharge tubesadapted to produce deionization of said discharge tubes.

2. The arrangement specified in claim 1 in which the magnetic couplingmeans for coupling the selective tuned receiving circuits to the gridsof the discharge tubes have the grid circuits tuned to the samefrequency as the receiving circuits.

3. A carrier signaling system comprising, in combination, wavegenerating meansincluding an electron tube having a plurality of gridand anode elements mounted in a common sealed envelope and includingindividual circuits connected to said elements adapted to generateoscillations of a plurality of predetermined frequencies, an energysource for said tube, individual oscillation circuits included in eachof ing means upon operation of any one of the.

keying means thereby conditioning the selected grid circuits to providefor the generation of oscillations of a selected one of saidpredetermined frequencies as long as the selected keying means remainsoperated.

4. In a carrier telegraph system a twochannel receiving arrangementincluding, in combination, two selective receiving circuits each tunedto an individual frequency, selective signal translating means, andselective signal amplifying means including an electronic amplifyingtube ,provided with twin control grids connected respectively in saidselective receiving circuits and also having twin anodes, said grids andanodes being immersed in a common atmosphere and sealed in a commonenvelope, two electronic discharge tubes each provided with controlgrids and adapted to be ionized uponthe application of a critical valueof potential to their control grids, and individually tuned magneticcoupling means .for coupling the anode circuits of said amplifying tubeto the control grids of said discharge tubes, said tuned circuit of themagnetic coupling means being characterized by a controlled small L/Cratio adapted to retard the resonant response of said tuned circuit.

5. In carrier signal terminal apparatus adapted to function selectivelyfor sending and receiving, in combination, an electronic dischargedevice having a plurality of grid and anode elements mounted in a'commonsealed envelope and including individual circuits connected to saidelements, individual tuned circuits included in each of the gridcircuits and including means for normally conditioning the device toprevent current flow in the anode circuits, individual keying meansincluded in the said grid circuits and signal translating meanscontrolled by the said anode circuits, positionable switching means tocondition selectively the said device and said associated circuitswhereby in one position the keying means are effective to initiateselectively carrier signals of predetermined frequencies and in anotherposition condition the same said elements of the device and associatedcircuits to amplify selectively signals of the aforesaid predeterminedfrequencies on receiving thereby controlling selectively the operationof the said translating means.

6. In carrier signal terminal apparatus adapted to function selectivelyfor sending and receiving, in combination, signal translating means,selectively tuned electronic relay means adapted to selectively actuatesaid signal translating means, an electronic discharge device having aplurality of grid and anode elements mounted in a common sealed envelopeand including individual circuits connected to said elements, individualtuned circuits and individual keying means included in each of the gridcircuits, and positionable switching means to condition selectively thesaid device and associated element circuits whereby in one positionselective operation of the keying means are effective to initiateselectively carrier signals of predetermined frequencies, and in anotherposition condition the same said elements of the device and associatedcircuits to amplify selectively signals of the aforesaid predeterminedfrequencies thereby controlling selectively the operation of the saidelectronic relay means and associated translating means.

HARRY J. NICHOLS. HENRY L. THOLSTRUP.

